Use EventEmitter.removeListener instead of the nonexistent 'off' method

method.

Without this patch, you get an error that looks like this:

TypeError: Object #<ReadStream> has no method 'off'
    at null.action (/Users/duncan/git/duncanmak/test-project/node_modules/rx/rx.node.js:145:24)
    at Disposable.dispose (/Users/duncan/git/duncanmak/test-project/node_modules/rx/rx.js:612:18)
    at SingleAssignmentDisposablePrototype.dispose (/Users/duncan/git/duncanmak/test-project/node_modules/rx/rx.js:701:17)
    at AutoDetachObserverPrototype.dispose (/Users/duncan/git/duncanmak/test-project/node_modules/rx/rx.js:4668:20)
    at SingleAssignmentDisposablePrototype.dispose (/Users/duncan/git/duncanmak/test-project/node_modules/rx/rx.js:701:17)
    at AutoDetachObserverPrototype.dispose (/Users/duncan/git/duncanmak/test-project/node_modules/rx/rx.js:4668:20)
    at CompositeDisposablePrototype.dispose (/Users/duncan/git/duncanmak/test-project/node_modules/rx/rx.js:554:39)
    at null.action (/Users/duncan/git/duncanmak/test-project/node_modules/rx/rx.binding.js:524:49)
    at Disposable.dispose (/Users/duncan/git/duncanmak/test-project/node_modules/rx/rx.js:612:18)
    at SingleAssignmentDisposablePrototype.dispose (/Users/duncan/git/duncanmak/test-project/node_modules/rx/rx.js:701:17)